Golf balls are formed from a variety of compositions, which provides a golf ball manufacturer the ability to alter feel and aerodynamic characteristics of a particular ball. For example, golf ball covers formed from balata allow a highly skilled golfer to achieve spin rates sufficient to more precisely control ball direction and distance, particularly on shorter shots. Balata covered golf balls are easily damaged, however, which discourages the average golfer from using such balls. To remedy this durability issue, manufacturers typically use ionomer resin as a cover material. However, while ionomer resin covered golf balls possess virtually cut-proof covers, the spin and feel are inferior compared to balata covered balls.
Polyurethanes and polyureas have also been recognized as useful materials for golf ball covers since the resulting golf balls are durable like ionomer resin, but have the softer feel of a balata covered golf ball. U.S. Pat. No. 4,123,061 teaches a golf ball made from a polyurethane prepolymer formed of polyether with diisocyanate that is cured with either a polyol or an amine-type curing agent. In addition, U.S. Pat. No. 5,334,673 discloses the use of two categories of polyurethane available on the market, i.e., thermoset and thermoplastic polyurethanes, for forming golf ball covers and, in particular, thermoset polyurethane covered golf balls made from a composition of polyurethane prepolymer and a slow-reacting amine curing agent, and/or a difunctional glycol. U.S. Pat. No. 5,484,870 discloses a polyurea composition comprising the reaction product of an organic diisocyanate and an organic amine, each having at least two functional groups. Once these two ingredients are combined, the reaction rate is very fast and, thus, the ability to vary the physical properties of the composition is limited.
Despite the favorable characteristics of polyurethane and polyurea materials for use in golf balls, ball components formed of these materials do not fully match ionomer resin golf ball components with respect to resilience or the rebound (a function of the initial velocity of a golf ball after impact with a golf club). In addition, in order to achieve even adequate resilience and shear resistance, manufacturers are generally limited to material hardness ranges of 30 Shore D or greater. Moreover, manufacturing in the lower range of this hardness results in a high degree of non-concentric ball components due to viscosity issues. Furthermore, while the spin rates of polyurethane and polyurea covered golf balls are higher than ionomer covered balls, achieving an even high spin rate would provide more control.
Therefore, there remains a continuing need for golf equipment and, in particular, golf balls having components formed from materials that provide the desired soft feel and, thus, higher spin, but still have at least comparable resilience to that of ionomer resins without adversely affecting overall performance characteristics of the golf balls.